Ruthenocenes and Half‐Open Ruthenocenes: Synthesis, Characterization, and Their Use as CVD Precursors for Ruthenium Thin Film Deposition

Abstract

AbstractConsecutive synthesis methodologies for the preparation of a series of trimethylsilyl and tert‐butyl‐substituted ruthenocenes of the type Ru(η5‐C5H3R1R2)(η5‐C5H3R3R4) (2, R1 = SiMe3, R2 = R3 = R4 = H; 3, R1 = R3 = SiMe3, R2 = R4 = H; 4, R1 = R2 = R3 = SiMe3, R4 = H; 5, R1 = R2 = R3 = R4 = SiMe3; 6, R1 = R3 = tBu, R2 = R4 = H; 7, R1 = R3 = tBu, R2 = SiMe3, R4 = H; 8, R1 = R3 = tBu, R2 = R4 = SiMe3) and Ru(η5‐2,3‐Me2C5H5)(η5‐C5H4R) (10, R = tBu; 12, R = SiMe3) are discussed and their use as a MOCVD precursor for the deposition of ruthenium is reported. The molecular structures of 3, 5–8, 10, and 12 in the solid state are reported. The half‐open ruthenocenes 10 and 12, which are liquids at ambient temperature, exhibit significantly shorter Ru–centroid (η5‐2,3‐Me2C5H5) bond lengths in contrast to ruthenocenes 3 and 5–8. The thermal behavior of all ruthenocenes was studied by thermogravimetric analysis showing that they evaporate without decomposition at atmospheric pressure. In addition, vapor pressure measurements were carried out to obtain profound information about the volatility of the synthesized sandwich compounds. The highest vapor pressures were found for 10 and 12. It was observed that the higher the number of SiMe3 groups, the higher the deposition temperature. All compounds were applied as precursors in MOCVD. The depositions on Si/SiO2 targets were carried out in a vertical cold‐wall CVD reactor between 633 and 688 K with a flow rate of 50 mL min–1 using nitrogen as the carrier gas and oxygen as the coreactant (50 mL min–1). With the tBu‐functionalized ruthenocenes 6 and 10 ruthenium thin films were obtained, while mixed ruthenium/SiO2 layers were formed with 2, 7, 8, and 12. The appropriate layers possess thicknesses between 75–135 nm and are conformal and dense as proven by SEM, EDX spectroscopy, and XPS studies.